An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector consisting of an ink pressurization chamber, an ejecting actuator and a nozzle through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the pressurization chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the recording medium is moved relative to the printhead.
Inkjet ink includes a variety of volatile and nonvolatile components including pigments or dyes, humectants, image durability enhancers, and carriers or solvents. A key consideration in ink formulation and ink delivery is the ability to produce high quality images on the print medium. Image quality can be degraded if evaporation of volatile components in the vicinity of the nozzle causes the viscosity to increase too much. The maintenance station of the printer typically includes a cap that surrounds the printhead die nozzle face during periods of nonprinting in order to inhibit evaporation of the volatile components of the ink, and also to provide protection against accumulation of particulates on the nozzle face. The maintenance station also typically includes a wiper for wiping the nozzle face to clean off ink residue and other debris.
A common type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the recording medium and the printhead is mounted on a carriage. In a carriage printer, the recording medium is advanced a given distance along a media advance direction and then stopped. While the recording medium is stopped, the printhead is moved by the carriage in a carriage scan direction that is substantially perpendicular to the media advance direction as the drops are ejected from the nozzles. After the printhead has printed a swath of the image while traversing the recording medium, the recording medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
In an inkjet printer, the face of the printhead die containing the nozzle array(s) is typically positioned near the recording medium in order to provide improved print quality. Close positioning of the nozzle face of the printhead die to the recording medium keeps the printed dots close to their intended locations, even for angularly misdirected jets. A printed wiring member that brings electrical signals to the printhead die is typically attached adjacent to the printhead die and is electrically interconnected to the printhead die. The electrical interconnections are subsequently encapsulated for protection.
In order to provide the capability of printing across the entire width of the recording medium, and also to allow space for the carriage to decelerate and stop before changing directions to print the next swath, typically the carriage moves the printhead beyond the side edges of the recording medium. Generally the position of the recording medium relative to the printhead nozzle face is fairly well controlled. However, occasionally a sheet of recording medium can have a dog-eared edge. Also occasionally multiple sheets of recording medium can be inadvertently fed at the same time, sometimes resulting in paper jamming and folding in accordion fashion. In such situations, the close proximity of the printhead nozzle face to the nominal position of the recording medium can result in recording medium striking the nozzle face of the die as the carriage moves the printhead past the edge of the recording medium. For nozzle faces made of material that is fragile or brittle, such strikes can cause catastrophic damage to the printhead, requiring its replacement. Several patents including U.S. Pat. Nos. 7,018,503, 6,902,260, 5,751,324, and 4,500,895 disclose mounting the printhead die within a recess in the mounting substrate. Such a recess at the mounting substrate can help protect the printhead die, but can add manufacturing complexities.
Commonly assigned U.S. Pat. No. 7,862,147, incorporated herein in its entirety by reference, discloses providing inclined surfaces near the printhead die to protect the nozzle face from damaging impact by recording medium. The printed wiring member attached adjacent to the printhead die is typically a flexible circuit that is thinner than printhead die. An embodiment is described in U.S. Pat. No. 7,862,147 where a shim is provided underneath the flexible circuit to bring the surface of the flexible circuit to a similar height as the nozzle face of the printhead die and the tops of the inclined surfaces. This provides further protection, as well as improved maintainability of the printhead. When maintaining the nozzle face in the printer, a wiper is used to wipe excess ink and other debris off the nozzle face as well as off the flexible circuit that is typically used as a capping surface for the maintenance station cap to seal against. Shimming the flexible circuit so that it is at a similar height as the nozzle face allows the wiper blade to wipe flexible circuit as well as the nozzle face.
A similar raising of the height of the wiring member relative to nozzle face of the printhead die is described in U.S. Pat. No. 6,659,591, where a ceramic plate is used to raise the electrical wiring member so that electrical connections between the electrical wiring member and the printhead die can be done in a planar manner. This is appropriate if tape automated bonding is used to connect electrical traces that cantilever beyond the edge of the electrical wiring member, as in U.S. Pat. No. 6,659,591. However, if wire bonding is used to electrically interconnect the wiring member and the printhead die, the wire loops can extend to a height above the nozzle face surface such that after the wire bonds are encapsulated, the encapsulation can interfere with wiping, and can also prevent the positioning of the printhead nozzle face as close to the nominal position of the recording medium as would otherwise be desired. In addition, the encapsulant material, which is applied as a liquid, is relatively unconstrained in this arrangement and flow of the encapsulant needs to be carefully controlled.
What is needed is a configuration of the printhead that provides protection for the printhead die, a lower encapsulant height where wire bonding is used to provide electrical interconnection between the printhead die and the flexible circuit, a more well-controlled flow of the encapsulant material, and a capping surface that can be readily wiped at the same time as the printhead nozzle face.